Although these studies suggest that variations in maternal care influence play behavior, it is AbMole Seratrodast important to note that the dams in these studies also displayed other differences in maternal care, like time spent in the nest or the time spent arched-back nursing. As such, it is still unclear whether the somatosensory stimulation associated with maternal grooming is specifically responsible for the differences seen in juvenile social play behavior. Juvenile social play behavior in rats, which is thought to be one of the earliest non-mother directed social behaviors, involves a complex set of behaviors that seem to be modulated by several brain regions and neurobiological systems. The brain regions that influence juvenile play behavior have mainly been elucidated by lesion studies. For example, damaging the cortex, mediobasal hypothalamus, nucleus accumbens, or amygdala will result in decreased social play. The AbMole Capromorelin tartrate importance of the amygdala has been further elucidated by studies that examine region specificity. During the juvenile period, males engage in higher levels of social play behavior than females, and testosterone treatment directly into the developing amygdala is sufficient to fully masculinize social play behavior in females. This suggests that the amygdala plays an important role in sexually differentiating juvenile social play behavior. While organization of sex differences in juvenile social play behavior is influenced by the endogenous steroid hormones, other research has indicated that neurotransmitters are also important in controlling juvenile social play behavior, such as dopamine and serotonin. Indeed, pharmacologically altering dopamine signaling can enhance juvenile social play behavior ; whereas, serotonin, which plays an important role in the regulation of aggression, appears to have an inverse relationship with social play behavior. Although several neurobiological substrates can regulate social play, it is unclear how maternal care impacts these systems to alter juvenile social play. The following study examines whether only manipulating the amount of somatosensory stimulation associated with maternal grooming is sufficient to alter juvenile social play and some neurobiological substrates associated with juvenile social play within the juvenile amygdala. We report that variations in maternal contact during the neonatal period can modify the sex difference typically seen in juvenile social play behavior. By only manipulating the amount of somatosensory stimulation received by the pups, our results lend strong support to the concept that the amounts of infant contact received by the pup can program later juvenile social play behavior. Interestingly, giving extra tactile stimulation to neonatal males decreased juvenile social play compared to control males. Altering the amount of tactile stimuli given to female neonates did not alter their later levels of juvenile social play. These data indicate that differences in the levels of maternal grooming between males and females may act to prevent overt sex differences in juvenile social interactions. Additionally, maternal stimuli selectively altered aspects of the serotonin system within the juvenile male amygdala, but not in females. Specifically, simulating maternal grooming in males eliminated the sex difference observed in 5HT2a mRNA levels.